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What not to plant

Purple loosestrife can choke out native plants in wetland areas, affecting food sources and cover for wildlife. It is most problematic in the Northeast and Upper Midwest. To get rid of it, pull it out (it's tough), burn it, or apply glyphosate herbicide.

How invasive plants take root

Maybe kudzu on your neighbor's land is creeping onto your own, or perhaps purple loosestrife is choking your backyard pond. The causes of both these problems and countless more are the result of non-native plants finding their way into places they don't belong. And while invasive species may wreak havoc on your garden or your yard, they can also destroy entire ecosystems.

According to The Nature Conservancy (TNC), more than 4,500 foreign species (including plants, animals, and insects) have made themselves at home in the U.S. in the last century. You're probably aware of many of them. But others aren't so obvious. Did you know English ivy is considered a problem-causing invasive? Kudzu is another offender, which has taken over thousands of acres all over the South since its introduction as an erosion controller and ornamental in the 1870s.

"Invasive is a sophisticated word for weed," notes John Peter Thompson, an owner of Behnke Nurseries in Beltsville, Maryland, and secretary of the National Invasive Species Council Advisory Committee. "A weed is a wrong plant in the wrong place that crowds out other plants. Invasives, if left unchecked, can eventually create biological deserts."

How do they get here?
Invasive species have many routes into American ecosystems. John Randall, director of TNC's Global Invasive Species Initiative, says they can come into places they don't belong as contaminant in seed, grain, or hay. They have also migrated in the ballast of ships, and some have been intentionally introduced as ornamental garden plants or to serve practical purposes as windbreaks or for erosion control.

Individuals may also unwittingly spread invasive species, whether plants or insects, with something as simple as not cleaning hiking boots between hikes and transferring soil matter from one part of the country to another. "If you have a home in the Midwest and you travel to your vacation cabin in Maryland with a cord of wood," says Thompson, "you may bring the emerald ash borer with you."